If you are eligible to take part in this study, you will have surgery to place a catheter into the ommaya reservoir. The ommaya reservoir is a catheter system that allows drugs to be administered directly to parts of the brain. In this study, the catheter will be used to collect about 1 teaspoon of cerebrospinal fluid (CSF - the fluid surrounding the brain and spinal cord) to check the status of the disease and for the infusion of methotrexate directly into the 4th ventricle of the brain, which is 1 of the 4 connected fluid-filled cavities in the brain.